Development of Bexarotene Analogs for Treating Cutaneous T-Cell Lymphomas

Bexarotene, a drug approved for treatment of cutaneous T-cell lymphoma (CTCL), is classified as a rexinoid by its ability to act as a retinoid X receptor (RXR) agonist with high specificity. Rexinoids are capable of inducing RXR homodimerization leading to the induction of apoptosis and inhibition of proliferation in human cancers. Numerous studies have shown that bexarotene is effective in reducing viability and proliferation in CTCL cell lines. However, many treated patients present with cutaneous toxicity, hypothyroidism, and hyperlipidemia due to crossover activity with retinoic acid receptor (RAR), thyroid hormone receptor (TR), and liver X receptor (LXR) signaling, respectively. In this study, 10 novel analogs and three standard compounds were evaluated side-by-side with bexarotene for their ability to drive RXR homodimerization and subsequent binding to the RXR response element (RXRE). In addition, these analogs were assessed for proliferation inhibition of CTCL cells, cytotoxicity, and mutagenicity. Furthermore, the most effective analogs were analyzed via qPCR to determine efficacy in modulating expression of two critical tumor suppressor genes, ATF3 and EGR3. Our results suggest that these new compounds may possess similar or enhanced therapeutic potential since they display enhanced RXR activation with equivalent or greater reduction in CTCL cell proliferation, as well as the ability to induce ATF3 and EGR3. This work broadens our understanding of RXR-ligand relationships and permits development of possibly more efficacious pharmaceutical drugs. Modifications of RXR agonists can yield agents with enhanced biological selectivity and potency when compared to the parent compound, potentially leading to improved patient outcomes.

Abstract 1118: The novel rexinoid V-125 reduces tumor growth in the MMTV-Neu model of breast cancer and the A/J model of lung cancer via immunomodulation

Rexinoids are ligands which selectively bind to and activate Retinoid X Receptors (RXRs), regulating the transcription of genes involved in several cancer-relevant biological processes. Rexinoids have anti-neoplastic activity with low toxicities in multiple preclinical studies. Bexarotene, used to treat cutaneous T cell lymphoma, is the only FDA-approved rexinoid. Bexarotene has also been evaluated in clinical trials for metastatic breast cancer and non-small-cell lung carcinoma. Subsets of patients in these trials exhibited clinical responses despite advanced, late-stage disease and refractoriness to prior therapy. By modifying structures of known efficacious rexinoids, we can improve potency, increase selectivity for RXR, and minimize toxicity. We have screened a series of novel rexinoids, which are selective for RXR with minimal off-target activation. V-125 was selected as our lead based on its performance in an optimized in vitro screening paradigm. V-125 displayed potent anti-inflammatory activity without elevating triglycerides, a known adverse effect of other rexinoids. To validate our screening paradigm, the tumor-preventive effects of V-125 were assessed in two clinically relevant mouse models: the MMTV-Neu model of HER2+ breast cancer and the A/J model of lung carcinogenesis. V-125 significantly (p < 0.001) increased tumor-free survival of MMTV-Neu mice in comparison to controls, resulting in a ~10 week increase in mean time to tumor development. In A/J mice, V-125 significantly (p < 0.05) reduced lung surface tumor number, size, and burden without increasing plasma triglycerides. To assess the treatment efficacy of V-125, MMTV-neu mice with established tumors were treated with V-125 or control diet. Overall survival was significantly (p < 0.05) higher in mice treated with V-125 than the control. To characterize the mechanism of V-125, we evaluated a mouse breast cancer PCR array, which demonstrated that V-125 downregulates IL-6 mRNA expression in MMTV-Neu tumors over three-fold, suggesting that V-125 modulates crosstalk between cancer cells and immune cells. We have previously shown that rexinoids alter immune cell populations in tumors and modulate secretion of inflammatory cytokines. A growing body of literature also suggests that RXR plays a role in regulating phenotype and function of macrophages. To test the hypothesis that V-125 modulates macrophage populations in the tumor microenvironment, we evaluated the ability of V-125 to differentially skew tumor-educated macrophages. Bone marrow-derived macrophages were stimulated with conditioned media from MMTV-Neu tumor cells and treated with V-125, and the expression of phenotypic markers was assessed by qPCR. These studies provide insight into the mechanism of V-125, which has the potential to be effective in reducing cancer growth.

Citation Format: Lyndsey Reich, Jessica Moerland, Ana S. Leal, Di Zhang, Sarah Carapellucci, Carl E. Wagner, Karen Liby. The novel rexinoid V-125 reduces tumor growth in the MMTV-Neu model of breast cancer and the A/J model of lung cancer via immunomodulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1118.

Rexinoids Modulate Effector T Cell Expression of Mucosal Homing Markers CCR9 and α4β7 Integrin and Direct Their Migration In Vitro

Altering T cell trafficking to mucosal regions can enhance immune responses towards pathogenic infections and cancers at these sites, leading to better outcomes. All-trans-retinoic acid (ATRA) promotes T cell migration to mucosal surfaces by inducing transcription of the mucosal-homing receptors CCR9 and α4β7 via binding to retinoic acid receptors (RARs), which heterodimerize with retinoid X receptors (RXRs) to function. However, the unstable nature and toxicity of ATRA limit its use as a widespread treatment modality for mucosal diseases. Therefore, identifying alternatives that could reduce or eliminate the use of ATRA are needed. Rexinoids are synthetically derived compounds structurally similar to ATRA. Originally named for their ability to bind RXRs, rexinoids can enhance RAR-mediated gene transcription. Furthermore, rexinoids are more stable than ATRA and possess an improved safety profile, making them attractive candidates for use in clinical settings. Here we show that select novel rexinoids act as ATRA mimics, as they cause increased CCR9 and α4β7 expression and enhanced migration to the CCR9 ligand, CCL25 in vitro, even in the absence of ATRA. Conversely, other rexinoids act synergistically with ATRA, as culturing cells with suboptimal doses of both compounds resulted in CCR9 expression and migration to CCL25. Overall, our findings show that rexinoids can be used independently or synergistically with ATRA to promote mucosal homing of T cells in vitro, and lends support for the prospective clinical use of these compounds in immunotherapeutic approaches for pathogenic infections or cancers at mucosal surfaces.

The rexinoid V-125 reduces tumor growth in preclinical models of breast and lung cancer

Rexinoids are ligands which activate retinoid X receptors (RXRs), regulating transcription of genes involved in cancer-relevant processes. Rexinoids have anti-neoplastic activity in multiple preclinical studies. Bexarotene, used to treat cutaneous T cell lymphoma, is the only FDA-approved rexinoid. Bexarotene has also been evaluated in clinical trials for lung and metastatic breast cancer, wherein subsets of patients responded despite advanced disease. By modifying structures of known rexinoids, we can improve potency and toxicity. We previously screened a series of novel rexinoids and selected V-125 as the lead based on performance in optimized in vitro assays. To validate our screening paradigm, we tested V-125 in clinically relevant mouse models of breast and lung cancer. V-125 significantly (p < 0.001) increased time to tumor development in the MMTV-Neu breast cancer model. Treatment of established mammary tumors with V-125 significantly (p < 0.05) increased overall survival. In the A/J lung cancer model, V-125 significantly (p < 0.01) decreased number, size, and burden of lung tumors. Although bexarotene elevated triglycerides and cholesterol in these models, V-125 demonstrated an improved safety profile. These studies provide evidence that our screening paradigm predicts novel rexinoid efficacy and suggest that V-125 could be developed into a new cancer therapeutic.

Modeling, Synthesis, and Biological Evaluation of Potential Retinoid-X-Receptor (RXR) Selective Agonists: Analogs of 4-[1-(3,5,5,8,8-Pentamethyl-5,6,7,8-tetrahyro-2-naphthyl)ethynyl]benzoic Acid (Bexarotene) and 6-(Ethyl(4-isobutoxy-3-isopropylphenyl)amino)nicotinic Acid (NEt-4IB)

Five novel analogs of 6-(ethyl)(4-isobutoxy-3-isopropylphenyl)amino)nicotinic acid—or NEt-4IB—in addition to seven novel analogs of 4-[1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)ethynyl]benzoic acid (bexarotene) were prepared and evaluated for selective retinoid-X-receptor (RXR) agonism alongside bexarotene (1), a FDA-approved drug for cutaneous T-cell lymphoma (CTCL). Bexarotene treatment elicits side-effects by provoking or disrupting other RXR-dependent pathways. Analogs were assessed by the modeling of binding to RXR and then evaluated in a human cell-based RXR-RXR mammalian-2-hybrid (M2H) system as well as a RXRE-controlled transcriptional system. The analogs were also tested in KMT2A-MLLT3 leukemia cells and the EC₅₀ and IC₅₀ values were determined for these compounds. Moreover, the analogs were assessed for activation of LXR in an LXRE system as drivers of ApoE expression and subsequent use as potential therapeutics in neurodegenerative disorders, and the results revealed that these compounds exerted a range of differential LXR-RXR activation and selectivity. Furthermore, several of the novel analogs in this study exhibited reduced RARE cross-signaling, implying RXR selectivity. These results demonstrate that modification of partial agonists such as NEt-4IB and potent rexinoids such as bexarotene can lead to compounds with improved RXR selectivity, decreased cross-signaling of other RXR-dependent nuclear receptors, increased LXRE-heterodimer selectivity, and enhanced anti-proliferative potential in leukemia cell lines compared to therapeutics such as 1.

Evaluating Novel RXR Agonists That Induce ApoE and Tyrosine Hydroxylase in Cultured Human Glioblastoma Cells

There is considerable interest in identifying effective and safe drugs for neurodegenerative disorders. Cell culture and animal model work have demonstrated that modulating gene expression through RXR-mediated pathways may mitigate or reverse cognitive decline. However, because RXR is a dimeric partner for several transcription factors, activating off-target transcription is a concern with RXR ligands (rexinoids). This off-target gene modulation leads to unwanted side effects that can include low thyroid function and significant hyperlipidemia. There is a need to develop rexinoids that have binding specificity for subsets of RXR heterodimers, to drive desired gene modulation, but that do not induce spurious effects. Herein, we describe experiments in which we analyze a series of novel and previously reported rexinoids for their ability to modulate specific gene pathways implicated in neurodegenerative disorders employing a U87 cell culture model. We demonstrate that, compared to the FDA-approved rexinoid bexarotene (1), several of these compounds are equally or more effective at stimulating gene expression via LXREs or Nurr1/NBREs and are superior at inducing ApoE and/or tyrosine hydroxylase (TH) gene and protein expression, including analogs 8, 9, 13, 14, 20, 23, and 24, suggesting a possible therapeutic role for these compounds in Alzheimer's or Parkinson's disease (PD). A subset of these potent RXR agonists can synergize with a presumed Nurr1 ligand and antimalarial drug (amodiaquine) to further enhance Nurr1/NBREs-directed transcription. This novel discovery has potential clinical implications for treatment of PD since it suggests that the combination of an RXR agonist and a Nurr1 ligand can significantly enhance RXR-Nurr1 heterodimer activity and drive enhanced therapeutic expression of the TH gene to increase endogenous synthesis of dopamine. These data indicate that is it possible and prudent to develop novel rexinoids for testing of gene expression and side effect profiles for use in potential treatment of neurodegenerative disorders, as individual rexinoids can have markedly different gene expression profiles but similar structures.

Addition of rexinoids during T cell activation enhances mucosal-homing receptor expression and migratory ability of effector cells in vitro

Certain vitamins directly impact immune cell migration, indicating potential to function as a vaccine adjuvant. We previously showed that all-trans retinoic acid (ATRA), the biologically active form of vitamin A, modifies gut-homing receptor expression on effector T cells upon binding to the retinoic acid receptor (RAR), which joins with the retinoid X receptor (RXR) to function. Giving ATRA during vaccination also resulted in enhanced mucosal protection following viral challenge in murine models. While promising, certain factors limit adding ATRA to a vaccine, including its instability and poor solubility. Rexinoids, synthetic ligands for the RXR, may mimic or better ATRA immune effects by enhancing RAR-mediated transcription. Their improved stability and solubility also indicates a greater potential for clinical use. Here we explored the ability of different rexinoids to program effector T cell expression of gut-homing receptors CCR9, a4b7, and CD103. Naïve T cells from transgenic mice were activated with appropriate peptide and set concentration of each rexinoid. Flow cytometric analysis showed increased expression of gut-homing receptors in the presence of select rexinoids, indicating their ability to act as an ATRA mimic. A cooperative relationship was seen between other rexinoids and ATRA as co-culturing with suboptimal doses of each showed enhanced receptor expression, suggesting they could potentially act with ATRA normally found in serum. Some rexinoids also promoted better effector T cell migration compared to ATRA, following analysis of a transwell migration assay. Overall, our findings support the prospective use of rexinoids as adjuvants during vaccination.

Novel Vaccine Adjuvants: Exploring the Potential of Rexinoids to Influence Effector T Cell Homing to Mucosal Sites

Vaccines are the most successful defense against infectious diseases. Effective vaccines must target induced immune responses to areas of pathogen entry, a primary site being mucosal surfaces. Certain vitamins can directly impact immune cell migration, indicating potential to function as an adjuvant. We previously showed that all-trans retinoic acid (ATRA), the biologically active form of vitamin A, modifies gut-homing receptor expression on effector T cells upon binding to the retinoic acid receptor (RAR), which joins with the retinoid X receptor (RXR) to function. Giving ATRA during vaccination also resulted in enhanced mucosal protection following viral challenge in murine models. While promising, certain factors limit adding ATRA to a vaccine, including its instability and poor solubility. Rexinoids, synthetic ligands for the RXR, could mimic or better ATRA immune effects by enhancing RAR-mediated transcription. Their improved stability and solubility also allows a greater potential for clinical use. Here we explored the ability of different rexinoids to program effector T cell expression of gut-homing receptors CCR9, α4β7, and CD103. Naïve T cells from transgenic mice were activated with peptide and set concentration of each rexinoid. Flow cytometry showed increased expression of gut-homing receptors in the presence of select rexinoids, indicating their ability to act as an ATRA mimic. A cooperative relationship was also seen between other rexinoids and ATRA as co-culturing with suboptimal doses of each showed enhanced receptor expression, suggesting these rexinoids could potentially act with ATRA normally found in serum. Overall, our findings support the prospective use of rexinoids as adjuvants during vaccination.

Testing Novel Pyrimidinyl Rexinoids: A New Paradigm for Evaluating Rexinoids for Cancer Prevention

Rexinoids, selective ligands for retinoid X receptors (RXR), have shown promise in preventing many types of cancer. However, the limited efficacy and undesirable lipidemic side-effects of the only clinically approved rexinoid, bexarotene, drive the search for new and better rexinoids. Here we report the evaluation of novel pyrimidinyl (Py) analogues of two known chemopreventive rexinoids, bexarotene (Bex) and LG100268 (LG268) in a new paradigm. We show that these novel derivatives were more effective agents than bexarotene for preventing lung carcinogenesis induced by a carcinogen. In addition, these new analogues have an improved safety profile. PyBex caused less elevation of plasma triglyceride levels than bexarotene, while PyLG268 reduced plasma cholesterol levels and hepatomegaly compared with LG100268. Notably, this new paradigm mechanistically emphasizes the immunomodulatory and anti-inflammatory activities of rexinoids. We reveal new immunomodulatory actions of the above rexinoids, especially their ability to diminish the percentage of macrophages and myeloid-derived suppressor cells in the lung and to redirect activation of M2 macrophages. The rexinoids also potently inhibit critical inflammatory mediators including IL6, IL1β, CCL9, and nitric oxide synthase (iNOS) induced by lipopolysaccharide. Moreover, in vitro iNOS and SREBP (sterol regulatory element-binding protein) induction assays correlate with in vivo efficacy and toxicity, respectively. Our results not only report novel pyrimidine derivatives of existing rexinoids, but also describe a series of biological screening assays that will guide the synthesis of additional rexinoids. Further progress in rexinoid synthesis, potency, and safety should eventually lead to a clinically acceptable and useful new drug for patients with cancer.

Methods to Generate an Array of Novel Rexinoids by SAR on a Potent Retinoid X Receptor Agonist: A Case Study with NEt-TMN

The methods described in this chapter concern procedures for the design, synthesis, and in vitro biological evaluation of an array of potent retinoid-X-receptor (RXR) agonists employing 6-(ethyl(5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-yl)amino)nicotinic acid (NEt-TMN), and recently reported NEt-TMN analogs, as a case study. These methods have been extensively applied beyond the present case study to generate several analogs of other potent RXR agonists (rexinoids), particularly the RXR agonist known as bexarotene (Bex), a Food and Drug Administration (FDA) approved drug for cutaneous T-cell lymphoma that is also often prescribed, off-label, for breast, lung, and other human cancers. Common side effects with Bex treatment include hypertriglyceridemia and hypothyroidism, because of off-target activation or inhibition of other nuclear receptor pathways impacted by RXR. Because rexinoids are often selective for RXR, versus the retinoic-acid-receptor (RAR), cutaneous toxicity is often avoided as a side effect for rexinoid treatment. Several other potent RXR agonists, and their analogs, have been reported in the literature and rigorously evaluated (often in comparison to Bex) as potential cancer therapeutics with unique activity and side-effect profiles. Some of the more prominent examples include LGD100268, CD3254, and 9-cis-UAB30, to name only a few. Hence, the methods described herein are more widely applicable to a diverse array of RXR agonists.In terms of design, the structure-activity relationship (SAR) study is usually performed by modifying three distinct areas of the rexinoid base structure, either of the nonpolar or polar sides of the rexinoid and/or the linkage that joins them. For the synthesis of the modified base-structure analogs, often identical synthetic strategies used to access the base-structure are applied; however, reasonable alternative synthetic routes may need to be explored if the modified analog intermediates encounter bottlenecks where yields are negligible for a given step in the base-structure route. In fact, this particular problem was encountered and successfully resolved in our case study for generating an array of NEt-TMN analogs.

Dataset on the response of Hut78 cells to novel rexinoids

This article presents the experimental data supporting analysis of differential gene expression of human cutaneous T cell lymphoma (CTCL) cell culture cells (Hut78) treated with bexarotene or a variety of rexinoids, in conjunction with "A Novel Gene Expression Analytics-based Approach to Structure Aided Design of Rexinoids for Development as Next-Generation Cancer Therapeutics" (Hanish et al. 2018). Data presented here include microarray gene expression analysis of a subset of genes. A novel method for analyzing gene expression in the context of a model of ligand mechanism, called the Divergence Score, is described. Analysis to identify the presence of potential retinoid response elements in putative promoter regions of the study genes is also presented.

A novel gene expression analytics-based approach to structure aided design of rexinoids for development as next-generation cancer therapeutics

Rexinoids are powerful ligands that bind to retinoid-X-receptors (RXRs) and show great promise as therapeutics for a wide range of diseases, including cancer. However, only one rexinoid, bexarotene (Targretin TM) has been successfully transitioned from the bench to the clinic and used to treat cutaneous T-cell lymphoma (CTCL). Our goal is to develop novel potent rexinoids with a less untoward side effect profile than bexarotene. To this end, we have synthesized a wide array of rexinoids with EC50 values and biological activity similar to bexarotene. In order to determine their suitability for additional downstream analysis, and to identify potential candidate analogs for clinical translation, we treated human CTCL cells in culture and employed microarray technology to assess gene expression profiles. We analyzed twelve rexinoids and found they could be stratified into three distinct categories based on their gene expression: similar to bexarotene, moderately different from bexarotene, and substantially different from bexarotene. Surprisingly, small changes in the structure of the bexarotene parent compound led to marked differences in gene expression profiles. Furthermore, specific analogs diverged markedly from our hypothesis in expression of genes expected to be important for therapeutic promise. However, promoter analysis of genes whose expression was analyzed indicates general regulatory trends along structural frameworks. Our results suggest that certain structural motifs, particularly the basic frameworks found in analog 4 and analog 9, represent important starting points to exploit in generating additional rexinoids for future study and therapeutic applications.

Mucins and Their Role in Shaping the Functions of Mucus Barriers

We review what is currently understood about how the structure of the primary solid component of mucus, the glycoprotein mucin, gives rise to the mechanical and biochemical properties of mucus that are required for it to perform its diverse physiological roles. Macroscale processes such as lubrication require mucus of a certain stiffness and spinnability, which are set by structural features of the mucin network, including the identity and density of cross-links and the degree of glycosylation. At the microscale, these same features affect the mechanical environment experienced by small particles and play a crucial role in establishing an interaction-based filter. Finally, mucin glycans are critical for regulating microbial interactions, serving as receptor binding sites for adhesion, as nutrient sources, and as environmental signals. We conclude by discussing how these structural principles can be used in the design of synthetic mucin-mimetic materials and provide suggestions for directions of future work in this field.

Using Rexinoids to Program Effector T cells for Homing to Mucosal Sites of Virus Transmission

Vaccines are the most effective defense against infectious diseases. To be most successful, vaccines must target the induced immune response to chief sites of pathogen entry: epithelial and mucosal surfaces. We have previously shown that the biologically active form of Vitamin A, all-trans retinoic acid (ATRA), can directly modulate the expression of gut mucosal-homing receptors on T cells as binding of ATRA to the retinoic acid receptor (RAR), which partners with the retinoid X receptor (RXR), promotes transcription of specific genes. Rexinoids, synthetic ligands for the RXR, have potential to mimic or improve the immune effects of vitamin A by enhancing RAR-mediated transcription. Additionally, rexinoids have a greater potential for clinical use due to their improved solubility and stability, making them candidates to incorporate into vaccines. Here, we explored the possibility of different rexinoids to function as adjuvants during vaccination to program effector T cell expression of the gut-homing receptors CCR9, α4β7, and CD103. CD8 T cells obtained from transgenic mice were co-cultured with peptide and set concentration of each rexinoid, followed by flow cytometric analysis of receptor expression. We observed increased expression of gut-homing receptors during activation in the presence of certain rexinoids, indicating that they can mimic the effects of ATRA. Furthermore, we saw a cooperative relationship between other rexinoids and ATRA, as co-culturing with sub-optimal doses of each resulted in enhanced expression. Our findings lend support for the prospective use of these rexinoids as adjuvants during vaccination and in therapeutic approaches against diseases transmitted across mucosal surfaces.

Molecular dynamics simulations and molecular flooding studies of the retinoid X-receptor ligand binding domain

Bexarotene is an FDA approved retinoid X-receptor (RXR) agonist for the treatment of cutaneous T-cell lymphoma, and its use in other cancers and Alzheimer's disease is being investigated. The drug causes serious side effects, which might be reduced by chemical modifications of the molecule. To rationalize known agonists and to help identify sites for potential substitutions we present molecular simulations in which the RXR ligand-binding domain was flooded with a large number of drug-like molecules, and molecular dynamics simulations of a series of bexarotene-like ligands bound to the RXR ligand-binding domain. Based on the flooding simulations, two regions of interest for ligand modifications were identified: a hydrophobic area near the bridgehead and another near the fused ring. In addition, positional fluctuations of the phenyl ring were generally smaller than fluctuations of the fused ring of the ligands. Together, these observations suggest that the fused ring might be a good target for the design of higher affinity bexarotene-like ligands, while the phenyl ring is already optimized. In addition, notable differences in ligand position and interactions between the RXRα and RXRβ were observed, as well as differences in hydrogen bonding and solvation, which might be exploited in the development of subspecies-specific ligands.

Retinoid X Receptor Selective Agonists and their Synthetic Methods

Since the isolation and identification of the retinoid X receptor (RXR) as a member of the nuclear receptor (NR) superfamily in 1990, its analysis has ushered in a new understanding of physiological regulation by nuclear receptors, and novel methods to identify other unknown and orphan receptors. Expression of one or more of the three isoforms of RXR-α, β, and γ-can be found in every human cell type. Biologically, RXR plays a critical role through its ability to partner with other nuclear receptors. RXR is able to regulate nutrient metabolism by forming "permissive" heterodimers with peroxisome proliferator-activated receptor (PPAR), liver-X-receptor (LXR), farnesoid X receptor (FXR), pregnane X receptor (PXR) and constitutive androstane receptor (CAR), which function when ligands are bound to one or both of the heterodimer partners. Conversely, RXR is able to form "nonpermissive" heterodimers with vitamin D receptor (VDR), thyroid receptor (TR) and retinoic acid receptor (RAR), which function only in the presence of vitamin D, T3 and retinoic acid, respectively. Furthermore, RXR can form homodimers in the presence of a selective agonist, or rexinoid, to regulate gene expression and to either inhibit proliferation or induce apoptosis in human cancers. Thus, over the last 25 years there have been several reports on the design and synthesis of small molecule rexinoids. This review summarizes the synthetic methods for several of the most potent rexinoids thus far reported.

Aspartate β-hydroxylase modulates cellular senescence through glycogen synthase kinase 3β in hepatocellular carcinoma

Aspartate β-hydroxylase (ASPH) is an enzyme overexpressed in human hepatocellular carcinoma (HCC) tumors that participates in the malignant transformation process. We determined if ASPH was a therapeutic target by exerting effects on cellular senescence to retard HCC progression. ASPH knockdown or knockout was achieved by short hairpin RNAs or the CRISPR/Cas9 system, respectively, whereas enzymatic inhibition was rendered by a potent second-generation small molecule inhibitor of ASPH. Alterations of cell proliferation, colony formation, and cellular senescence were evaluated in human HCC cell lines. The potential mechanisms for activating cellular senescence were explored using murine subcutaneous and orthotopic xenograft models. Inhibition of ASPH expression and enzymatic activity significantly reduced cell proliferation and colony formation but induced tumor cell senescence. Following inhibition of ASPH activity, phosphorylation of glycogen synthase kinase 3β and p16 expression were increased to promote senescence, whereas cyclin D1 and proliferating cell nuclear antigen were decreased to reduce cell proliferation. The mechanisms involved demonstrate that ASPH binds to glycogen synthase kinase 3β and inhibits its subsequent interactions with protein kinase B and p38 upstream kinases as shown by coimmunoprecipitation. In vivo experiments demonstrated that small molecule inhibitor treatment of HCC bearing mice resulted in significant dose-dependent reduced tumor growth, induced phosphorylation of glycogen synthase kinase 3β, enhanced p16 expression in tumor cells, and promoted cellular senescence.

CONCLUSIONS

We have identified a new mechanism that promotes HCC growth and progression by modulating senescence of tumor cells; these findings suggest that ASPH enzymatic activity is a novel therapeutic target for HCC.

Analysis of differential secondary effects of novel rexinoids: select rexinoid X receptor ligands demonstrate differentiated side effect profiles

In order to determine the feasibility of utilizing novel rexinoids for chemotherapeutics and as potential treatments for neurological conditions, we undertook an assessment of the side effect profile of select rexinoid X receptor (RXR) analogs that we reported previously. We assessed pharmacokinetic profiles, lipid and thyroid-stimulating hormone (TSH) levels in rats, and cell culture activity of rexinoids in sterol regulatory element-binding protein (SREBP) induction and thyroid hormone inhibition assays. We also performed RNA sequencing of the brain tissues of rats that had been dosed with the compounds. We show here for the first time that potent rexinoid activity can be uncoupled from drastic lipid changes and thyroid axis variations, and we propose that rexinoids can be developed with improved side effect profiles than the parent compound, bexarotene (1).

Thrombocytopenia in Patients with Gastric Varices and the Effect of Balloon-occluded Retrograde Transvenous Obliteration on the Platelet Count

OBJECTIVES

Gastric varices primarily occur in cirrhotic patients with portal hypertension and splenomegaly and thus are probably associated with thrombocytopenia. However, the prevalence and severity of thrombocytopenia are unknown in this clinical setting. Moreover, one-third of patients after balloon-occluded retrograde transvenous obliteration (BRTO) have aggravated splenomegaly, which potentially may cause worsening thrombocytopenia. The aim of the study is to determine the prevalence and degree of thrombocytopenia in patients with gastric varices associated with gastrorenal shunts undergoing BRTO, to determine the prognostic factors of survival after BRTO (platelet count included), and to assess the effect of BRTO on platelet count over a 1-year period.

MATERIALS AND METHODS

This is a retrospective review of 35 patients who underwent BRTO (March 2008-August 2011). Pre- and post-BRTO platelet counts were noted. Potential predictors of bleeding and survival (age, gender, liver disease etiology, platelet count, model for end stage liver disease [MELD]-score, presence of ascites or hepatocellular carcinoma) were analyzed (multivariate analysis). A total of 91% (n = 32/35) of patients had thrombocytopenia (<150,000 platelet/cm(3)) pre-BRTO. Platelet counts at within 48-h, within 2 weeks and at 30-60 days intervals (up to 6 months) after BRTO were compared with the baseline pre-BRTO values.

RESULTS

35 Patients with adequate platelet follow-up were found. A total of 92% and 17% of patients had a platelet count of <150,000/cm(3) and <50,000/cm(3), respectively. There was a trend for transient worsening of thrombocytopenia immediately (<48 h) after BRTO, however, this was not statistically significant. Platelet count was not a predictor of post-BRTO rebleeding or patient survival. However, MELD-score, albumin, international normalized ratio (INR), and etiology were predictors of rebleeding.

CONCLUSION

Thrombocytopenia is very common (>90% of patients) in patients undergoing BRTO. However, BRTO (with occlusion of the gastrorenal shunt) has little effect on the platelet count. Long-term outcomes of BRTO for bleeding gastric varices using sodium tetradecyl sulfate in the USA are impressive with a 4-year variceal rebleed rate and transplant-free survival rate of 9% and 76%, respectively. Platelet count is not a predictor of higher rebleeding or patient survival after BRTO.

Modeling, synthesis, and biological evaluation of potential retinoid X receptor (RXR) selective agonists: novel analogues of 4-[1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)ethynyl]benzoic acid (bexarotene) and (E)-3-(3-(1,2,3,4-tetrahydro-1,1,4,4,6-pentamethylnaphthalen-7-yl)-4-hydroxyphenyl)acrylic acid (CD3254)

Three unreported analogues of 4-[1-(3,5,5,8,8-pentamethyl-5-6-7-8-tetrahydro-2-naphthyl)ethynyl]benzoic acid (1), otherwise known as bexarotene, as well as four novel analogues of (E)-3-(3-(1,2,3,4-tetrahydro-1,1,4,4,6-pentamethylnaphthalen-7-yl)-4-hydroxyphenyl)acrylic acid (CD3254), are described and evaluated for their retinoid X receptor (RXR) selective agonism. Compound 1 has FDA approval as a treatment for cutaneous T-cell lymphoma (CTCL), although treatment with 1 can elicit side-effects by disrupting other RXR-heterodimer receptor pathways. Of the seven modeled novel compounds, all analogues stimulate RXR-regulated transcription in mammalian 2 hybrid and RXRE-mediated assays, possess comparable or elevated biological activity based on EC50 profiles, and retain similar or improved apoptotic activity in CTCL assays compared to 1. All novel compounds demonstrate selectivity for RXR and minimal crossover onto the retinoic acid receptor (RAR) compared to all-trans-retinoic acid, with select analogues also reducing inhibition of other RXR-dependent pathways (e.g., VDR-RXR). Our results demonstrate that further improvements in biological potency and selectivity of bexarotene can be achieved through rational drug design.

Synthesis and biological evaluation of halogenated curcumin analogs as potential nuclear receptor selective agonists

This report describes the synthesis of analogs of curcumin, and their analysis in acting as nuclear receptor specific agonists. Curcumin (CM), a turmeric-derived bioactive polyphenol found in curry, has recently been identified as a ligand for the vitamin D receptor (VDR), and it is possible that CM exerts some of its bioeffects via direct binding to VDR and/or other proteins in the nuclear receptor superfamily. Using mammalian-two-hybrid (M2H) and vitamin D responsive element (VDRE) biological assay systems, we tested CM and 11 CM synthetic analogs for their ability to activate VDR signaling. The M2H assay revealed that RXR and VDR association was induced by CM and several of its analogs. VDRE-based assays demonstrated that pure curcumin and eight CM analogs activated transcription of a luciferase plasmid at levels approaching that of the endocrine 1,25 dihydroxyvitamin D(3) (1,25D) ligand in human colon cancer cells (HCT-116). Additional experiments were performed in HCT-116 utilizing various nuclear receptors and hormone responsive elements to determine the receptor specificity of curcumin binding. CM did not appear to activate transcription in a glucocorticoid responsive system. However, CM along with several analogs elicited transcriptional activation in retinoic acid and retinoid X receptor (RXR) responsive systems. M2H assays using RXR-RXR, VDR-SRC1 and VDR-DRIP revealed that CM and select analogs stimulate RXR homodimerization and VDR-coactivator interactions. These studies may lead to the discovery of novel curcumin analogs that activate nuclear receptors, including RXR, RAR and VDR, resulting in similar health benefits as those for vitamins A and D, such as lowering the risk of epithelial and colon cancers.

Modeling, synthesis and biological evaluation of potential retinoid X receptor-selective agonists: novel halogenated analogues of 4-[1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)ethynyl]benzoic acid (bexarotene)

The synthesis of halogenated analogues of 4-[1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)ethynyl]benzoic acid (1), known commonly as bexarotene, and their evaluation for retinoid X receptor (RXR)-specific agonist performance is described. Compound 1 is FDA approved to treat cutaneous T-cell lymphoma (CTCL); however, bexarotene treatment can induce hypothyroidism and elevated triglyceride levels, presumably by disrupting RXR heterodimer pathways for other nuclear receptors. The novel halogenated analogues in this study were modeled and assessed for their ability to bind to RXR and stimulate RXR homodimerization in an RXRE-mediated transcriptional assay as well as an RXR mammalian-2-hybrid assay. In an array of eight novel compounds, four analogues were discovered to promote RXR-mediated transcription with EC(50) values similar to that of 1 and are selective RXR agonists. Our approach also uncovered a periodic trend of increased binding and homodimerization of RXR when substituting a halogen atom for a proton ortho to the carboxylic acid on 1.

2-Fluoro-4-(methoxycarbonyl)benzoic acid

In the crystal of the title compound, C₉H₇FO₄, classical carboxylate inversion dimers are linked by pairs of O—H⋯O hydrogen bonds. The packing is consolidated by C—H⋯F and C—H⋯O interactions. The benzene ring and the methoxycarbonyl group are nearly coplanar, with a dihedral angle of 1.5 (3)° between them, whereas the carboxyl group has a dihedral angle of 20.2 (4)° with respect to the benzene ring.

Modeling, synthesis and biological evaluation of potential retinoid X receptor (RXR) selective agonists: novel analogues of 4-[1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)ethynyl]benzoic acid (bexarotene)

This report describes the synthesis of analogues of 4-[1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)ethynyl]benzoic acid (1), commonly known as bexarotene, and their analysis in acting as retinoid X receptor (RXR)-specific agonists. Compound 1 has FDA approval to treat cutaneous T-cell lymphoma (CTCL); however, its use can cause side effects such as hypothyroidism and increased triglyceride concentrations, presumably by disruption of RXR heterodimerization with other nuclear receptors. The novel analogues in the present study have been evaluated for RXR activation in an RXR mammalian-2-hybrid assay as well as an RXRE-mediated transcriptional assay and for their ability to induce apoptosis as well as for their mutagenicity and cytotoxicity. Analysis of 11 novel compounds revealed the discovery of three analogues that best induce RXR-mediated transcriptional activity, stimulate apoptosis, have comparable K(i) and EC(50) values to 1, and are selective RXR agonists. Our experimental approach suggests that rational drug design can develop new rexinoids with improved biological properties.

Synthesis and First Molecular Structure of a Bis-2-spiro-1-boraadamantane Derivative

[reaction: see text] A new method for synthesizing the 2-spiro-boraadamantane pyridine complex (2) from 1-ethynylcyclohexylmethyl ether has been developed. The chemistry has been applied to the synthesis of bis-2-spiro-1-boraadamantane.pyridine (1) from trans-1,4-diethynyl-1,4-dimethoxycyclohexane (8). This bis-Lewis acid serves as a self-assembling molecular building block with difunctional Lewis bases.

The Polyhomologation of 1-Boraadamantane: Mapping the Migration Pathways of a Propagating Macrotricyclic Trialkylborane

Trialkyl and triaryl organoboranes undergo multiple, repetitive homologations upon reaction with dimethylsulfoxonium methylide (1). This multiple homologation reaction, or polyhomologation, produces polymethylene in a living reaction. Applying the polyhomologation reaction to cyclic and polycyclic organoboranes permits the construction of unique oligomeric and polymeric architectures that are not readily accessible by standard olefin polymerization. The polyhomologation of 1-boraadamantane.THF (2) by ylide 1 generates novel macrotricyclic trialkylboranes (3). The oxidation of these macrocyclic organoboranes generates a three-armed star polymethylene polymer (4) incorporating a cis,cis-1,3,5-trisubstituted cyclohexane core. Interestingly, only one-third of the initiators lead to product formation, resulting in an observed degree of polymerization 3 times higher than expected. Close examination of the initial stages of polymerization show that 1-boraadamantane.THF reacts with 1 equiv of 1 to afford a monohomologated product. Subsequent homologations were found to contain branch points leading to isomeric tricyclic products after the third, fourth, and fifth methylene insertions. At these stages of homologation, all of the propagating species result in tricyclic trialkylborane cages with collapsed, inverted pyramidal boron centers that are substantially less reactive toward ylide. Approximately two-thirds of the species discontinue polymerization at these stages. However, one-third of these species continue to propagate and eventually result in the formation of giant macrotricyclic polymers of narrow polydispersity. Molecular modeling and kinetic simulation have aided in the analysis of the probable pathways through which the reaction proceeds.

Synthesis of 1-boraadamantaneamine derivatives with selective astrocyte vs C6 glioma antiproliferative activity. A novel class of anti-hepatitis C agents with potential to bind CD81

A variety of amine complexes with 1-boraadamatane were synthesized and subsequently evaluated for an antiproliferative effect on CD81-enriched cell lines to provide evidence for binding and activation of CD81. CD81 is a member of the tetraspanin family of membrane proteins found in all cell lineages in the liver. CD81 signals for antiproliferation when bound by antibodies. It is known that the HCV-E2 envelope glycoprotein binds to the CD81 protein. While it is unclear whether virus entry into host cells is directly linked to virus attachment via CD81 for HCV, this step in the viral life cycle has recently proven to be an effective point of attack for other viruses including HIV and rhinoviruses. The aim of the current study concerns the synthesis of amantidine analogues by appending primary amines to 1-boraadamantane to evaluate such compounds for CD81-dependent antiproliferation of CD81-enriched cell lines (astrocyte) vs CD81-deficient cell lines (C6 glioma). If the antiproliferative effect of these amantidine analogues proves to be an effect of binding and activating CD81, then these compounds may have the potential to prevent or treat HCV infections. Each compound's potential for preventive and therapeutic activity stems from the compound's potential to block viral attachment, virus-cell fusion, or virus entry into host cells or to counter potential mechanisms of HCV immune evasion. Out of a library of over 500 compounds, including randomly selected small molecules and rationally designed small molecules, only the 1-boraadamantaneamine compounds and structurally similar analogues display a significant antiproliferative effect on the CD81-enriched astrocytes relative to the CD81-deficient cell lines. In fact, 1-boraadamantane.l-phenylalanine methyl ester complex (5), 1-boraadamantane.ethanolamine complex (8), and (S)-2-[(adamantane-1-carbonyl)amino]-3-phenylpropionic acid (15) show a dose-dependent, astrocyte-selective antiproliferative activity in the concentration range 0.1-10 microM. This is consistent with the binding and activation of CD81 and represents a 2-fold improvement compared to the clinically prescribed anti-HCV agent, amantidine, in the same concentration range. Consequently, the 1-boraadamantaneamine derivatives present a promising lead in the development of small molecules with potential to bind to CD81 and treat HCV infections.

1-Boraadamantane blows its top, sometimes. The mono- and polyhomologation of 1-boraadamantane

[reaction: see text] 1-Boraadamantane.THF (3) reacts with 1 equiv of dimethylsulfoxonium methylide (4) to afford a monohomologated product. The polyhomologation of 1-boraadamantane.THF by ylide 4 followed by oxidative cleavage generates star polymethylene polymers incorporating a cyclohexane core. However, only one-third of the initiators lead to product formation, resulting in an observed degree of polymerization three times higher than expected. The polyhomologation of 3 was found to contain branch points after the fourth and fifth methylene insertions. At the branch points, the propagating species either terminate in tricyclic trialkylborane cages with collapsed, pyramidal inverted boron centers that are unreactive toward ylide or they continue in uninterrupted polymerization and eventually result in the formation of giant "tube-like" structures such as 5.

Do electroweak precision data and Higgs-mass constraints rule out a scalar bottom quark with mass of order 5 GeV?

We study the implications of a scalar bottom quark, with a mass of O (5 GeV), within the minimal supersymmetric standard model. Light sbottoms may naturally appear for large tan(beta) and, depending on the decay modes, may have escaped experimental detection. We show that a light sbottom cannot be ruled out by electroweak precision data and the bound on the lightest CP-even Higgs-boson mass. We infer that a light b scenario requires a relatively light scalar top quark whose mass is typically about the top-quark mass. In this scenario the lightest Higgs boson decays predominantly into b pairs and obeys the mass bound m(h) less, similar 123 GeV.

Low-energy supersymmetry and the Tevatron bottom-quark cross section

A long-standing discrepancy between the bottom-quark production cross section and predictions of perturbative quantum chromodynamics is addressed. We show that pair production of light gluinos, of mass 12 to 16 GeV, with two-body decays into bottom quarks and light bottom squarks, yields a bottom-quark production rate in agreement with hadron collider data. We examine constraints on this scenario from low-energy data and make predictions that may be tested at the next run of the Fermilab Tevatron collider.

Right-sided aorta: a cadaver report and brief discussion of human aortic arch anomalies

We observed an unusual right-sided aorta during routine laboratory dissection. The short aortic arch passed to the right side of the esophagus and trachea and had four branches, from proximal to distal: left common carotid, right common carotid, right subclavian, left subclavian arteries. The ligamentum arteriosum connected the pulmonary trunk to the left subclavian artery and lay to the left of the esophagus and trachea. The left recurrent laryngeal nerve passed under the ligamentum arteriosum while the right recurrent laryngeal nerve passed under the aortic arch. The descending thoracic aorta was situated near the midline, anterior to the vertebral bodies; consequently, the right posterior intercostal arteries were shorter than normal. The large veins of the thorax and the other thoracic organs appeared normal.

Subisthmic accessory thyroid gland in man: a case report and a review of thyroid anomalies

Morphological variations of the thyroid gland are common and generally occur superior to the gland, reflecting its developmental origin. In this report we describe an accessory lobe located inferior to both lateral lobes and the isthmus. The accessory lobe was supplied by a branch of the right inferior thyroid artery and its vein drained via the plexus thyroideus impar. A discussion of thyroid anomalies is presented and a system for classifying variations of thyroid anatomy is proposed.

An unusually long ligamentum arteriosum

During routine laboratory dissections an unusually long ligamentum arteriosum, measuring 40 mm, was observed. Apparently, such a length for an otherwise normal ligamentum has not been reported previously. Forty-three other ligamenta in adults and three in newborn or stillborn infants were also measured having a range of 8 mm to 24 mm (mean 15.47 mm) and 7.5 mm to 11 mm (mean 9.5 mm) respectively. Since short and long ligaments have been reported previously, both in the newborn as well as in the adult, the variability in length of this structure appears normal and without any functional significance.

Metallic dissolution of a civil war bullet embedded in a sternum

The contemporary trend of converting departments of anatomy into departments of cell biology has brought with it the task of examining archive collections and storage facilities to figure out how to best utilize the available space. During one such inspection at the University of Louisville School of Medicine, a human sternum containing a dull metal projectile was uncovered. The projectile was easy to characterize as a bullet that had been deeply embedded in the bone. Less clear, however, were the circumstances detailing how the bullet had become lodged in the sternum, or how long the sternum might have been in storage at the University of Louisville. Radiographs of the sternum revealed a halo of surrounding density that dissipated in intensity from the margins of the bullet. Our initial hypothesis was that lead had been leached from the bullet into the bone matrix. To better assess what in fact contributed to this density, the sternum and the bullet were analyzed by energy-dispersive spectroscopy (EDS) to determine their elemental composition. That the bullet was composed of lead and aluminum was not surprising, but the extent to which the presence and dissolution of the bullet had affected the composition of the bony sternum was not entirely expected. The contribution of metal ions from the bullet to the inorganic matrix of bone was most notable for aluminum but nearly negligible for lead. This finding confirmed that bone affinity for metals is dependent upon the metal and supports previous reports that have suggested that lead is released from bone as soluble blood product during bony remodeling, whereas aluminum results in a significant elevation of bone density.